Chrysotile asbestos treated with phosphoric acid as an adsorbent for ammonia nitrogen

Our plain-English summary of Chrysotile asbestos treated with phosphoric acid as an adsorbent for ammonia nitrogen, by C.P. Girotto, S.D. de Campos, É.A. de Campos (Heliyon, 2020).

The study

• Authors: C.P. Girotto, S.D. de Campos, É.A. de Campos
• Journal: Heliyon
• Published: 2020;6(2):e03397
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The purpose of this study was to find an alternative application for chrysotile asbestos, given that there is a complete structure of extraction and production of this class of serpentine minerals, but its use is banned for many applications. The idea was to obtain a compound that could immobilize phosphate by triggering a reaction between the magnesium oxide and hydroxide contained in the mineral, without causing phosphate leaching. To this end, chrysotile (Mg3SiO5(OH)4) was treated with phosphoric acid (H3PO4) in a molar ratio of 1:3 in an aqueous medium at 85 °C until the solvent evaporated, resulting in two different solid compounds, which were prepared in a similar manner. The first compound (cri/H3PO4 1:3)1, was obtained by rinsing and then heat-treating it at 150 °C for 6 h, while the second one, (cri/H3PO4 1:3)2, was rinsed after the heat treatment. Compound (cri/H3PO4 1:3)1 underwent partial leaching, while compound (cri/H3PO4 1:3)2 showed a mass increase of 48%, with the formation of crystalline magnesium pyrophosphate mixed with amorphous SiO2. The latter compound adsorbed N-NH3 at pH 10, following the pseudo-first-order model (activation energy = 8329 ± 1696 J mol-1). Equilibrium experiments, which were performed following Hill's sigmoidal type S2 isotherm model, indicated that the adsorption phenomenon was governed by two processes, i.e., complexation up to the inflection point (KH between 10.0 mg L-1 at 40 °C and 13.6 mg L-1 at 25 °C) followed by adsorption. The qmax varied from 18.0 to 19.6 mgN g-1 and the adsorbent was reusable, maintaining its initial adsorbent capacity during its first reuse. This material, which was tested on real effluents, presented a N-NH3 removal rate similar to that shown by the test solutions. The treatment of chrysotile with H3PO4 conducts it to a composite that adsorbs ammoniacal nitrogen at pH 10 and it is reusable maintaining the adsorption capacity.

© 2020 Published by Elsevier Ltd.

In plain English

This was a laboratory chemistry study from Brazil. It did not involve people and did not measure health effects. The authors treated chrysotile asbestos, donated by the Brazilian Chrysotile Institute, with phosphoric acid (a 1:3 molar ratio of chrysotile to acid) and heated it. Their aim was to find a new use for the mineral as a material that removes ammonia nitrogen from water. They compared two preparation methods. The method that heat-treated the product at 150 degrees Celsius for 6 hours before rinsing worked better. It removed 84.6% of ammonia in a test at pH 10, compared with 41.2% for the other method. Under the microscope the treated material was less fibrous, although fibers mixed into a compact material were still visible. Its maximum capacity ranged from 18.0 to 19.6 mg of nitrogen per gram, and it kept a similar capacity (19.0) when reused once. On a sample of effluent from a wastewater treatment plant in Umuarama, Brazil, it removed 85.2% of the ammonia nitrogen. The authors concluded that the material is a feasible alternative for removing ammonia nitrogen from real effluents and offers an alternative use for chrysotile.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory materials-chemistry experiment (preparation and testing of an adsorbent made from chrysotile); no human or animal subjects
• Who was studied: Chrysotile asbestos donated by the Brazilian Chrysotile Institute (IBC), Goiás, Brazil; the treated material was also tested on an effluent sample from the SANEPAR wastewater treatment plant in Umuarama, Paraná, Brazil
• Exposure: Chrysotile reacted with phosphoric acid at a 1:3 molar ratio in water at 85 degrees Celsius until the water evaporated, then heat-treated at 150 degrees Celsius for 6 hours (two methods, differing in whether rinsing came before or after heat treatment)
• Main results:
  • In an ammonia adsorption test at pH 10, the Method 1 compound removed 41.2% and the Method 2 compound removed 84.6%
  • The Method 2 compound showed a mass increase of 48% compared with the starting chrysotile
  • After reaction with phosphoric acid, the Method 2 material was less fibrous under the microscope, although fibers were still visible
  • Ammonia nitrogen adsorption by the Method 2 compound was best at pH 10
  • Maximum adsorption capacity of the Method 2 compound ranged from 18.0 to 19.6 mg per gram across 25, 30 and 40 degrees Celsius
  • The recovered (reused) adsorbent had an adsorption capacity of 19.0 mg per gram, which the authors described as similar to the original material
  • On the wastewater treatment plant effluent sample, the Method 2 compound removed 85.2% of the initial ammonia nitrogen
  • In the effluent sample, chemical oxygen demand fell by 24.6%, and color and turbidity fell by 46.7% and 50.4%
  • The acid treatment reduced specific surface area from 14.7 (chrysotile) to 3.2 square meters per gram (Method 2 compound)
• The authors' conclusion: The authors concluded that the Method 2 compound is a feasible alternative for removing ammonia nitrogen from real effluents, and that treating chrysotile with phosphoric acid offers an alternative use for the mineral
• Limitations the authors state:
  • The authors stated that the surface-area and porosity results were not favorable for use of the compound as an adsorbent
  • The authors stated that the real nature of the complex formed with ammonia nitrogen was difficult to determine

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Serpentine Group, Crystalline.

Related studies

• Effects of chrysotile and acid-treated chrysotile on macrophage cultures — E.G. Beck, P.F. Holt, et al. (1971)
• Efficient and versatile fibrous adsorbent based on magnetic amphiphilic composites of chrysotile/carbon nanostructures for the removal of ethynilestradiol — A.P. Teixeira, A.D. Purceno, et al. (2013)
• In vitro reactivity of alveolar macrophages and red blood cells with asbestos fibres treated with oxalic acid, sulfur dioxide and benzo-3,4-pyrene — M.C. Jaurand, L. Magne, et al. (1981)
• Mesotheliomas in rats following inoculation with acid-leached chrysotile asbestos and other mineral fibres — G. Monchaux, J. Bignon, et al. (1981)
• Chrysotile asbestos detoxification with a combined treatment of oxalic acid and silicates producing amorphous silica and biomaterial — A. Valouma, A. Verganelaki, et al. (2016)
• The combination of oxalic acid with power ultrasound fully degrades chrysotile asbestos fibres — F. Turci, M. Tomatis, et al. (2007)

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